SUMMARY Direct cardiac reprogramming to generated induced cardiomyocytes (iCMs) from fibroblasts has emerged as a promising therapeutic strategy for the treatment of heart failure, which is still the leading cause of mortality and morbidity in the developed country. While much is known regarding iCMs generated from mouse cells, the adaptation of direct cardiac reprogramming to human cells is hurdled with low efficiency and poor quality because of intrinsic differences between species. We recently reported the single cell transcriptomic analysis during human cardiac reprogramming and discovered that the insufficient generation of iCMs is associated with underdeveloped gene programs, such as ion channel and cell junction, suggesting that additional reprogramming factors regulating function of cardiomyocytes might be required. In this research program, we hypothesis that a novel reprogramming factor TBX20 plays an essential role to generate cardiomyocyte identity by establishing gene programs associated with cardiomyocyte function. In support of our hypothesis, our preliminary data have shown that TBX20 is largely under-expressed in human iCMs. While forced expression of TBX20 significantly enhanced reprogramming efficiency accompanied with activation of gene programs associated with cardiomyocyte function. To test the hypothesis, we propose to 1) further determine the impact of TBX20 on direct human cardiac reprogramming and 2) determine how TBX20 functions as an essential reprogramming factor during this process. The main objective of this proposal is to identify the critical role of TBX20 on regeneration of cardiomyocytes during direct cardiac reprogramming. The completion of this proposal will not only provide mechanistic insight into how cardiomyocyte identity can be regenerated by direct cardiac reprogramming but also enable us to generate functional-reliable cardiomyocytes directly from human non-myocytes for potential heart repair.